Hip fractures present a serious and debilitating condition. Approximately 20-30% of hip fractures in geriatric patients result in death each year and many of the patients who survive will experience a significant loss of function. Hip fracture patients also experience medical and often cognitive co-morbidities making them highly vulnerable to post-operative decline and poor outcomes. Hip fractures have been recognized as the osteoporosis related fracture with the highest associated cost and morbidity.
The number of hip fractures occurring in the United States exceeded 300,000 in 2011, and hip fracture incidence is expected to increase with the aging population. Indeed, as people live longer, the number of hip fractures in the world, estimated at 1.7 million in 1990 is expected to rise exponentially to 6.3 million by the year 2050. By 2050, the worldwide incidence of hip fracture is projected to increase by 240% in women and 310% in men.
Following a hip fracture, patients are more likely to experience a fall, which is itself likely to generate considerable additional medical costs and to possibly result in a fracture in the uninjured hip. In 2000, the total direct medical costs of all fall injuries for people 65 and older exceeded $19 billion: $0.2 billion for fatal falls, and $19 billion for nonfatal falls. By 2020, the annual direct and indirect cost of fall injuries is expected to reach $54.9 billion (in 2007 dollars). In 2002, about 22% of community-dwelling seniors reported falling in the previous year. Medicare costs per fall averaged between $9,113 and $13,507. Among community-dwelling older adults, fall-related injury is one of the 20 most expensive medical conditions.
FIG. 1, demonstrates how osteoporosis results in thinning and loss of trabeculae, with a net effect of loss of bone mass and volume fraction (BV/TV), loss of connectivity and increased slenderness ratio (l/r), with concomittant facilitation of failure of individual trabecular elements. Once osteoclasts have resorbed enough bone tissue to create a discontinuity in a trabecular element, that element can no longer support load. As the cross-struts between longitudinally oriented trabeculae become discontinuous, the remaining trabeculae become relatively longer. Since buckling and bending are the predominant modes of trabecular deformation and failure, these changes in the trabecular structure influence the mechanical behavior of cancellous bone in disproportion to the corresponding change in mineral mass. The buckling load for a trabecular column is proportional to EA/(l/r)2, where E is the modulus of elasticity of the bone tissue comprising the trabeculae, A is the cross-sectional area of the trabeculae and l/r, the slenderness ratio, is measured as the effective length to width ratio of the trabeculae.
One may seek to counteract the architecture deterioration by inserting a filler material in bulk into the proximal femur. This insertion will create a polymerized block of material that is predominantly isotropic in structural and material properties. FIG. 2 illustrates the insertion of an isotropic elastomeric compound into the proximal femur. Unfortunately, this isotropic character does not mirror the directional, anisotropic behavior characterized by the healthy trabecular architecture of the proximal femur. Anisotropic materials have increased resistance along certain directions, such as bone along the trabecular architecture of the proximal femur, or wood along its grain direction. Isotropic materials fail predominantly by shearing forces, while anisotropic materials can be made to be significantly more resistant to failure along a preferred material direction.
Accordingly, there exists a need for interventional apparatus, systems and methods which reduce hip fracture risk. Particularly, there exists a need for apparatus, systems and methods which provide adequate anisotropic structural support.